126 Self- Incompatibility in Hermaphrodite Plants 



with hybridity. It is well known that hybrids exhibit all grades of 

 vegetative vigour and sexual potency. Here the wide variations in 

 either vegetative or sexual development, or in both, indicate that 

 certain incompatible combinations of protoplasmic elements fail to give 

 harmonious development of the zygote. In a few cases and especially 

 where a character is vitally concerned with nutrition (as for example the 

 non-chlorophyll condition) there is evidently a selective death of zygotes 

 homozygous for this character (see Belling, 1918) bub as a rule de- 

 generation and 'impotence in hybrids seem to result from degrees of 

 dissimilarity in the relative constitutional organization and development 

 inherent in the respective parents. 



It is to be recognized that various grades of impotence may develop 

 in a good species through such variations in morphological sex differen- 

 tiation as are described by the term intersexualism. Intersexualism 

 differs from impotence in hybridity in that it exhibits a tendency to be 

 one-sided. Indeed dioecism may be described as a complete one-sided 

 and alternative impotence that has arisen out of hermapliroditism, 

 Intersexualism may occur in all grades or degrees as is shown by 

 Goldschmidt (1916, 1917), Banta (1916, 1918), and the writer (1919) 

 and is of course a widespread developmental process leading to 

 a complete sex differentiation of individuals as contrasted with the 

 differentiation of sex organs in a single individual. In respect to 

 specialization of the individual as a whole intersexualism is a period 

 of progressive variation. 



In intersexuality various grades of maleness and femaleness may 

 develop for individuals as wholes, or for particular sex organs as such. 

 What is perhaps the best analysis of such phenomena in Mendelian 

 terms (by Goldschmidt) recognizes that the assumed factors involved 

 are themselves variable, that maleness and femaleness are properties 

 of all cells, that the factors for sex are the same as factors for general 

 growth, and that these are subject to much variation in relative potency. 



There is therefore a decided analogy between the variations in the 

 physiological condition of sex organs as revealed by their relative func- 

 tioning in incompatibilities and those variations in the development of 

 sex organs that are recognized under the term intersexualism. 



Sex differentiation is hence widely variable in both its morphological 

 ■ and its physiological aspects. 



4. Sex-determination and sex-differentiation in hermaphrodites are 

 fundamentally a process of ontogenetic development, and may occur at 

 various stages in ontogeny. 



